Hydrogenation of dienes and the selectivity for partial hydrogenation on a molybdenum disulfide catalyst

Abstract

The reaction of butadiene with hydrogen/deuterium on molybdenum disulfide (MoS/sub 2/) proceeded via the sec.-butyl intermediate and yielded only 1-butene-3,4-d/sub 2/ and 1-butene-d/sub 0/. The hydrogenation of isoprene on MoS/sub 2/ yielded 2-methyl-1-butene about four times as fast as it gave 3-methyl-1-butene, as previously found for other heterogeneous catalysts and in opposition to available results for homogeneous catalysts, which have a high selectivity for 3-methyl-1-butene. Isomerization of 2-methyl-1-butene to 2-methyl-2-butene occurred via the carbonium ion mechanism. Deuteriation of isoprene yielded 2-methyl-1-butene-d/sub 2/ and 3-methyl-1-butene-d/sub 2/ in a process in which the adsorption of isoprene molecules with the double bond adjacent to the methyl group was apparently loose compared with the adsorption on the other side of the double bond. Deuteriation of pentadiene also showed the weakened adsorption at the double bond adjacent to the alkyl group. The steric effect in the selectivity of isoprene hydrogenation was confirmed by molecular orbital calculations. Graphs, tables, and 20 references.